Method and internal combustion engine for improving the efficiency of an SCR system

Abstract

The invention relates to a method for improving the efficiency of an SCR system of an exhaust gas aftertreatment system (5) of an internal combustion engine (1), and to an internal combustion engine (1), wherein an operating medium is metered in upstream of the SCR catalytic converter (2) of the SCR system in a normal operating mode, wherein the operating medium comprises a reducing agent or can be converted into a reducing agent, wherein the reducing agent is stored at least temporarily in an SCR catalytic converter (2) of the SCR system, wherein the method comprises the following steps: operating of the internal combustion engine (1) in the normal operating mode, defining of a determined control value (6) by way of determining of the mass of an exhaust gas component which is measured overall at a point in the course of the exhaust gas aftertreatment system (5) during a first measurement window, determining of a calculated control value (7) by way of calculating of the mass of the exhaust gas component which occurs overall at the point in the course of the exhaust gas aftertreatment system (5) during the first measurement window, determining of the deviation (8) between the determined control value and the calculated control value, checking whether the determined deviation lies within a predefined deviation range, adapting of the metering quantity of the operating medium if the determined deviation lies outside the deviation range.

Claims

1. A method for improving an efficiency of an SCR system of an exhaust gas aftertreatment system (5) of an internal combustion engine (1), taking into consideration a cross-sensitivity of an NOx sensor to NH.sub.3, wherein an operating medium is metered upstream of the SCR catalytic converter (2) of the SCR system in a normal operating mode which corresponds to its intended operation, wherein the operating medium contains a reducing agent or is converted into the reducing agent, wherein the reducing agent is stored at least temporarily in an SCR catalytic converter (2) of the SCR system, comprising the following steps: operating the internal combustion engine (1) in the normal operating mode, defining a determined control value (6) by way of determining a mass of an exhaust gas component recorded by an NOx sensor (4), which is measured overall at a point in the course of the exhaust gas aftertreatment system (5) during a first measurement window, determining a calculated control value (7) by way of calculating the mass of the exhaust gas component, which occurs overall at the point in the course of the exhaust gas aftertreatment system (5) during the first measurement window, determining a deviation (8) between the determined control value and the calculated control value, checking whether the determined deviation lies within a predefined deviation range, adapting the metering quantity of the operating medium when the determined deviation lies outside of the deviation range, wherein NOx slip is detected when the determined deviation of the further measurement window is less than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NOx slip is detected, the metering quantity of operating medium is increased, or that NH.sub.3 slip is detected when the determined deviation of the further measurement window is greater than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NH.sub.3 slip is detected, the metering quantity of operating medium is reduced.

2. The method according to claim 1, wherein at least one further determined control value is determined during at least one further measurement window, at least one further calculated control value is calculated during the at least one further measurement window, a deviation between the further determined control value and the further calculated control value is determined, it is checked whether the determined deviation lies within the predefined deviation range, or another predefined deviation range, and in that the metering quantity of the operating medium is adapted when the determined deviation lies outside of the deviation range.

3. The method according to claim 1, wherein each of the determined control values is formed from the measured values of the NOx sensor (4) downstream of the SCR system.

4. The method according to claim 1, wherein the reactions, relevant for the method, of the SCR catalytic converter (2), can, in addition to real operation, be calculated in a kinetic model, whereby the kinetic model corresponds to a mathematical model of the physical model of the SCR system used.

5. The method according to claim 1, wherein each of the calculated control values is calculated with a kinetic model, or that each of the calculated control values is calculated from a characteristic diagram based on test bench data.

6. The method according to claim 1, wherein the normal operating mode comprises at least one of: a stationary, a transient and a non-stationary operation of at least one of the internal combustion engine (1) and the exhaust gas aftertreatment system (5).

7. The method according to claim 1, wherein the deviation (8) between the determined control value and the calculated control value is determined according to the following rule: $\mathrm{Deviation}=\frac{\mathrm{control}{\mathrm{value}}_{\mathrm{determined}}}{\mathrm{control}{\mathrm{value}}_{\mathrm{calculated}}}$ where the deviation is the determined deviation, where control value.sub.determined is the determined control value, and where control value.sub.calculated is the calculated control value.

8. The method according to claim 1, wherein the deviation (8) is determined through comparison of the determined control value with the calculated control value, wherein the metering quantity of the operating medium remains unchanged when the determined control value is less than the calculated control value, and wherein the metering quantity of the operating medium is adapted when the determined control value is greater than the calculated control value.

9. The method according to claim 1, wherein each measurement window is defined by the reaching of an energy quantity converted by the internal combustion engine (1), wherein each measurement window begins at a starting point and ends at an end point when a particular calculated energy quantity is reached, or that each measurement window is defined by a duration of a continuously stationary operation of the internal combustion engine (1), wherein each measurement window begins when at least one of: the internal combustion engine (1) is in stationary operation and ends before the internal combustion engine (1) enters at least one of a non-stationary operation, a transient operation; and a predefined duration has been reached.

10. The method according to claim 9, wherein an energy quantity converted by the internal combustion engine (1) is at least one of: determined from a characteristic diagram of the operating point of the internal combustion engine, is calculated from a rotational speed of the internal combustion engine, and an injected fuel quantity MfFullnj, and is calculated according to the following rule: $\mathrm{EEng}=\int \mathrm{PwrEng}$ $\mathrm{PwrEng}=\frac{2.Math.\pi .Math.\mathrm{NEng}.Math.\mathrm{TqEng}}{60.Math.1000}$ where EEng denotes the energy quantity converted by the internal combustion engine (1) during a measurement window, where PwrEng denotes the engine power, where NEng denotes the engine speed, and and where TqEng denotes the engine torque.

11. The method according to claim 1, wherein a validity of each recorded measurement window is evaluated taking into consideration at least one validity parameter.

12. The method according to claim 11, wherein the measurement window is defined as at least one of: valid when the at least one validity parameter lies within a validity range for a certain duration during the measurement window, invalid when the at least one validity parameter lies outside of a validity range for a certain duration during the measurement window, and invalid when a predetermined number of times when the validity range is at least one of exceeded, fallen short of and infringed.

13. The method according to claim 1, wherein when the determined deviation of the first measurement window lies outside of the deviation range, the metering quantity is increased in comparison with the metering quantity in the normal operating mode, so that an adapted metering quantity is metered thereafter.

14. The method according to claim 1, wherein NOx slip is detected when the determined deviation of the further measurement window is greater than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been reduced, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NOx slip is detected, the metering quantity of operating medium is increased, NH.sub.3 slip is detected when the determined deviation of the further measurement window is less than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been reduced, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NH.sub.3 slip is detected, the metering quantity of operating medium is reduced.

15. The method according to claim 1, wherein NOx slip is detected when the further determined control value of the further measurement window is less than the determined control value of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NOx slip is detected, the metering quantity of operating medium is increased, or that NH.sub.3 slip is detected when the further determined control value of the further measurement window is greater than the determined control value of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NH.sub.3 slip is detected, the metering quantity of operating medium is reduced.

16. The method according to claim 1, wherein NOx slip is detected when the further determined control value of the further measurement window is greater than the determined control value of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been reduced, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NOx slip is detected, the metering quantity of operating medium is increased, NH.sub.3 slip is detected when the further determined control value of the further measurement window is less than the determined control value of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been reduced, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NH.sub.3 slip is detected, the metering quantity of operating medium is reduced.

17. The method according to claim 1, wherein the metering quantity is adapted by an adaptation factor, wherein the adaptation factor is a predefined value, or wherein the adaptation factor is dependent on the determined deviation.

18. An internal combustion engine (1) comprising an exhaust gas aftertreatment system (5) with an SCR system, wherein the internal combustion engine (1) is configured to carry out a method for improving an efficiency of the SCR system of the exhaust gas aftertreatment system (5) of the internal combustion engine (1), taking into consideration a cross-sensitivity of an NOx sensor to NH.sub.3, wherein an operating medium is metered upstream of the SCR catalytic converter (2) of the SCR system in a normal operating mode which corresponds to its intended operation, wherein the operating medium contains a reducing agent or is converted into a reducing agent, wherein the reducing agent is stored at least temporarily in an SCR catalytic converter (2) of the SCR system, comprising the following steps: operating the internal combustion engine (1) in the normal operating mode, defining a determined control value (6) by way of determining a mass of an exhaust gas component recorded by an NOx sensor (4), which is measured overall at a point in the course of the exhaust gas aftertreatment system (5) during a first measurement window, determining a calculated control value (7) by way of calculating the mass of the exhaust gas component which occurs overall at the point in the course of the exhaust gas aftertreatment system (5) during the first measurement window, determining a deviation (8) between the determined control value and the calculated control value, checking whether the determined deviation lies within a predefined deviation range, adapting the metering quantity of the operating medium when the determined deviation lies outside of the deviation range, wherein NOx slip is detected when the determined deviation of the further measurement window is less than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NOx slip is detected, the metering quantity of operating medium is increased, or that NH.sub.3 slip is detected when the determined deviation of the further measurement window is greater than the determined deviation of the preceding measurement window and when, in the preceding measurement window, the metering quantity has been increased, in comparison with the metering quantity in the normal operating mode or in comparison with the adapted metering quantity, wherein, when NH.sub.3 slip is detected, the metering quantity of operating medium is reduced.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention is now explained further with reference to exemplary, non-exclusive and/or non-limiting exemplary embodiments.

(2) FIG. 1 shows a schematic graphic representation of a first embodiment of an internal combustion engine according to the invention which is configured and/or suitable for carrying out the method according to the invention, and

(3) FIG. 2 shows a schematic flow chart of two variants of a first embodiment of the method according to the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

(4) Unless otherwise stated, the reference symbols correspond to the following components or method steps:

(5) Internal combustion engine 1, SCR catalytic converter 2, metering device 3, NOx sensor 4, exhaust gas aftertreatment system 5, determining a determined control value 6, determining a calculated control value 7, determining the deviation 8, checking whether the determined deviation lies within a predefined deviation range 9, maintenance of the metering quantity 10, adaptation of the metering quantity in a preceding measurement window already carried out 11, increase in the metering quantity 12, decision logic 13, reduction in the metering quantity 14, recording of a measurement window 15, yes 16, no 17, and validity check 18.

(6) FIG. 1 shows a schematic graphic representation of a first embodiment of an internal combustion engine 1 according to the invention which is configured and/or suitable for carrying out the method according to the invention.

(7) The embodiment comprises an internal combustion engine 1 and an exhaust gas aftertreatment system 5. The exhaust gas aftertreatment system 5 comprises a metering device 3, an SCR catalytic converter 2 and an NOx sensor 4.

(8) The exhaust gas aftertreatment system 5 can for example comprise further exhaust gas aftertreatment components, such as a diesel oxidation catalyst DOC, an NOx storage catalyst NSC, a diesel particle filter DPF and/or an ammonia slip catalyst ASC.

(9) In the normal operating mode, which corresponds to intended operation, an operating medium is metered upstream of the SCR catalytic converter 2. The operating medium contains a reducing agent or can be converted into a reducing agent. The reducing agent, in particular the ammonia NH.sub.3, is stored at least temporarily in the SCR catalytic converter 2.

(10) FIG. 2 shows a schematic flow chart of variants of a first embodiment of the method according to the invention.

(11) According to this flow chart, at the beginning of the method a measurement window is recorded. The measurement window can be defined, in a first variant of the first embodiment, through the stationary operation of the internal combustion engine 1 or, in a second variant of the first embodiment, through reaching of the energy quantity converted by the internal combustion engine 1.

(12) The validity of the measurement window is then checked. According to this embodiment, the measurement window is evaluated as invalid if a validity parameter, for example the average SCR catalytic converter temperature, the stored quantity of reducing agent or the NOx concentration upstream of the SCR catalytic converter, lies outside of a predefined validity range for a certain duration during the measurement window.

(13) If the measurement window is evaluated as valid, a determined control value and a calculated control value are determined during the measurement window. The determined control value is defined by determining the mass of an exhaust gas component, in particular the emissions recorded by an NOx sensor, which is measured overall at a point in the course of the exhaust gas aftertreatment system 5 during the measurement window. The calculated control value is determined by calculating the mass of the exhaust gas component, in particular the NOx emissions, which occurs overall at the point in the course of the exhaust gas aftertreatment system during the measurement window.

(14) In a first variant of the first embodiment, after determining the calculated control values 7 the deviation between the determined control value and the calculated control value is determined and it is checked whether the determined deviation lies within a predefined deviation range.

(15) In order to determine the deviation between the determined control value and the calculated control value, the deviation between these two control values is calculated. In particular, the deviation is calculated according to the following rule:

(16) $\mathrm{Deviation}=\frac{\mathrm{control}{\mathrm{value}}_{\mathrm{determined}}}{\mathrm{control}{\mathrm{value}}_{\mathrm{calculated}}}$
whereby the deviation is the determined deviation, where control value.sub.determined is the determined control value, and where control value.sub.calculated is the calculated control value.

(17) If the calculated deviation lies within the deviation range, the metering quantity of the operating medium remains unchanged.

(18) If the calculated deviation lies outside of the deviation range, the metering quantity of the operating medium is changed. It is hereby checked, in a next step of the method, whether or not an adaptation of the metering quantity in comparison with the metering quantity in the normal operating mode has already been carried out 11 in a preceding measurement window.

(19) If no adaptation of the metering quantity of the operating medium has taken place yet, the metering quantity is, in a first step, increased in comparison with the metering quantity in the normal operating mode. As a result, an adapted metering quantity is thereafter introduced into the exhaust gas aftertreatment system 5, in particular upstream of the SCR catalytic converter 2.

(20) If an adaptation of the metering quantity of the operating medium has already taken place in a preceding measurement window, in a next step of the method the metering quantity is increased or reduced based on a decision logic 13.

(21) The metering quantity is increased according to the decision logic 13 and NOx slip detected if the calculated deviation of the further measurement window is less than the calculated deviation of the preceding measurement window and the metering quantity in the preceding measurement window has been increased in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(22) The metering quantity is reduced according to the decision logic 13 and NH.sub.3 slip detected if the calculated deviation of the further measurement window is greater than the calculated deviation of the preceding measurement window and the metering quantity in the preceding measurement window has been increased in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(23) The metering quantity is increased according to the decision logic 13 and NOx slip detected if the calculated deviation of the further measurement window is greater than the calculated deviation of the preceding measurement window and the metering quantity in the preceding measurement window has been reduced in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(24) In a second variant of the first embodiment, after determining the calculated control value 7 the deviation between the determined control value and the calculated control value is determined and it is checked whether the determined deviation lies within a predefined deviation range.

(25) In order to determine the deviation between the determined control value and the calculated control value, the determined control value and the calculated control value are compared with one another. According to this variant, the metering quantity of the operating medium remains unchanged if the determined control value is less than the calculated control value and as a result the determined deviation lies within a predefined deviation range. Otherwise, the metering quantity of the operating medium is adapted if the determined control value is greater than the calculated control value and as a result the determined deviation lies outside of a predefined deviation range.

(26) In a next step of the method, it is hereby checked whether or not an adaptation of the metering quantity in comparison with the metering quantity in the normal operating mode has already been carried out 11 in a preceding measurement window.

(27) If no adaptation of the metering quantity of the operating medium has taken place yet, the metering quantity is, in a first step, increased in comparison with the metering quantity in the normal operating mode. As a result, an adapted metering quantity is thereafter introduced into the exhaust gas aftertreatment system 5, in particular upstream of the SCR catalytic converter 2.

(28) If an adaptation of the metering quantity of the operating medium has already taken place 11 in a preceding measurement window, in a next step of the method the metering quantity is increased or reduced based on a decision logic 13.

(29) The metering quantity is increased according to the decision logic 13 and NOx slip detected if the further determined control value of the further measurement window is less than the determined control value of the preceding measurement window and the metering quantity in the preceding measurement window has been increased in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(30) The metering quantity is reduced according to the decision logic 13 and NH.sub.3 slip detected if the further determined control value of the further measurement window is greater than the determined control value of the preceding measurement window and the metering quantity in the preceding measurement window has been increased in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(31) The metering quantity is increased according to the decision logic 13 and NH.sub.3 slip detected if the further determined control value of the further measurement window is less than the determined control value of the preceding measurement window and the metering quantity in the preceding measurement window has been reduced in comparison with the metering quantity in the normal operating mode or in comparison with an already adapted metering quantity.

(32) In both variants of the first embodiment, the method is to be repeated after the metering quantity has been maintained, increased or has been reduced. For this purpose, on each renewed performance of the method a further measurement window is recorded and a further determined control value and a further calculated control value are determined and the further method steps carried out analogously to the preceding sequence.

(33) As a result it is possible to adjust the metering quantity of operating medium is efficiently as possible.

(34) The effects according to the invention can be achieved through this exemplary configuration.

(35) The invention is not limited to the embodiments described, but comprises any method and any internal combustion engine 1 according to the following claims.